The present invention relates to a method of and an apparatus for controlling height of a vehicle having a vehicle height adjusting device.
Conventional motor vehicles are known that have a vehicle height adjusting device to control the height of a vehicle to zones such as high, medium or low. Motor vehicles are also known that monitor the vehicle height at a high resolution (such as in millimeter units, for example) and that independently adjust the height for each of the four wheels. Such vehicles are disclosed in Japanese Patent Laid-Open No. 139709/1987.
In motor vehicles provided with suspension stroke sensors to detect the up-and-down relative displacement or stroke of the suspension units of each of the four wheels, suspension stroke information detected by each of the suspension sensors is used as the basis for performing vehicle height control independently for each of the suspension units. In this type of vehicles that has an active suspension, each suspension unit operates to achieve control to be in agreement with a reference vehicle height when there is a vehicle distortion or skewing, or when the degrees of wear of the tires are different. This causes imbalances between the contact loads of the wheels with the road surface.
As will be described later in detail with reference to he drawings, when the vehicle body is distorted, the suspension units of the left and right front wheels and the left and right rear wheels operate to cause the suspension lengths to take a set value or a reference vehicle height, so that whether the vehicle is running or stationary, the contact loads of one pair of diagonally opposite wheels are increased and the contact loads of the other pair of diagonally opposite wheels are decreased.
If an imbalance in the contact loads occurs as described above, the vehicle will become unstable and will tend to tilt with respect to a line connecting the points of contact with the road surface, of the diagonally opposing pair of wheels for which the suspension units are contracted.
Such an imbalance of the contact loads of the wheels occurs not only when there is distortion or skewing of the vehicle body and when there is tire wear, but also when there is deformation in the sensor links of the suspension stroke sensors, and when the vehicle stops on a distorted road surface.